Position measuring device and method for determining an absolute position

ABSTRACT

A position measuring apparatus with
         at least one material measure comprised of an optical structure of an arrangement of 3-D reflectors,   at least one light receiver arranged at a distance from the material measure,   a light source arranged at a distance from the material measure and at a distance from the light receiver, and   at least one transparent substrate present between the material measure and the light receiver, wherein the light receiver is deposited directly on the transparent substrate, on the side of the substrate opposite the material measure in the form of a thin-film structure consisting of several layers arranged one above another.       

     A supporting plate is provided with circuit-board conductors, on which the substrate is arranged, wherein the transparent substrate and the supporting plate are joined solidly together by a Flip-Chip assembly process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase entry under 35 U.S.C. §371 ofPCT/CH2011/000186 filed Aug. 19, 2011, which claims priority to SwissPatent Application No. 1342/10 filed Aug. 19, 2010, Swiss PatentApplication No. 1341/10 filed Aug. 19, 2010, and Swiss PatentApplication No. 1343/10 filed Aug. 20, 2010, the entirety of each ofwhich is incorporated by this reference.

FIELD OF THE INVENTION

The invention relates to a position measuring device and a method fordetermining the absolute position of a moving.

PRIOR ART

A sensor head of a sensor operating with reflected light is known fromUS patent application No. 2006/0007541. This sensor head has a lightsource, which projects a light beam onto a material measure, and twosemiconductor substrates. The semiconductor substrates each comprisephotodetectors, for detecting light that is reflected by the materialmeasure. Light source and semiconductor substrates are arranged in abox-like housing, wherein the light source is arranged and secured onthe bottom of the housing and the semiconductor substrates are arrangedand secured on the cover, with which the housing can be sealed. Thesemiconductor substrates are fastened by means of reversible assembly onthe cover.

The semiconductor substrates with the photodetectors are arrangedopposite one another on both sides of the light source in a directionthat is perpendicular to the direction of motion of the materialmeasure. Each semiconductor substrate has an electric circuit, and theelectric circuits of the two semiconductor substrates are connectedtogether by electric lines, which are formed on the underside of thecover. Current-voltage converters are formed directly on thesemiconductor substrates, in order to keep interferences as small aspossible.

A disadvantage of the known sensor head is that it is expensive toproduce. First, the semiconductor substrates must be fabricated and thenfastened to the housing cover. Then the light source is arranged andsecured at the bottom of the housing. Finally, the cover is fitted onthe housing in such a way that the light source is correctly oriented tothe semiconductor substrate. This must be carried out with the necessaryprecision, so that with relative movement of the material measure,signals (in particular the analogue signals to be worked up by thesensor system) of adequate quality can be obtained, so that the encoderfunctions perfectly. Making the electrical connections to the twosemiconductor substrates is also complicated and expensive. With such anarrangement, miniaturization of the sensor head cannot be achievedwithout loss of signal quality.

The device should be as compact as possible in its dimensions, so as tobe suitable for the construction of small encoders. Despite the verycompact design, it should still be able to make accurate determinationof the absolute position (even in the position at rest) possible, whichrequires production of a qualitatively good basic signal.

Another aim of the present invention is to provide a position measuringdevice that is economical to manufacture. The design of the deviceshould, moreover, make it insensitive to environmental influences. Inaddition, it should have a small power requirement, i.e. it should besuitable for operation with batteries.

SUMMARY OF THE INVENTION

By using a material measure with optical elements that make the totalluminous energy incident on the individual graduations available forforming the basic signal, and through compact design of the sensor head,which creates short light paths between light source and light receiver,economical use of the luminous energy becomes possible.

The function of the sensor head is established by a lithography step, bywhich a light source and light receiver elements are formed on the glasssubstrate. In the FlipChip process the glass substrate is arranged onthe supporting plate. The light receiver elements are connected viastud-bump and circuit-board conductors directly to a decoding circuitarranged on the back of the supporting plate.

In order to produce good basic signals, a special arrangement of thelight receiver elements is provided. These are mounted end-to-endfollowing the pattern A+b−a−B+. Careful layout of the light receivers isnecessary for correct distribution of the centres of gravity of thelight receiver elements. Moreover, the special shape provided plays adecisive role.

A compact design is made possible by using FlipChip assembly and otherprecautions. These are for example the choice of the metallic top layerof the light receiver elements, the use of stud-bumps for stableelectrical connection (for a stable basic signal) and the use of anadhesive technology, wherein a rather unusual permanent resist permitssecure adhesion. With this manner of construction, it is possible towork at low temperatures, which is gentle on the light receivers.

Owing to these precautions it is possible to construct a 3-channelabsolute encoder with a diameter from 4 to 20 mm. Thanks to the optimumlayout of the light paths, such an encoder can function with a powerrequirement of less than 3 or even 1 mA and achieve high resolutions ata reasonable price.

According to one aspect of the invention, the very small sensor head ismounted on a moving part, e.g. a lever, which makes it possible todetermine the absolute position e.g. of a motor shaft in its position atrest.

Configurations of the position measuring device are described below,wherein the aforesaid features—provided they are not mutuallyexclusive—can be implemented in any combination.

Furthermore, a position measuring device (such as an encoder) has thefollowing components:

-   -   a support,    -   a sensor head with a light source and a light receiver element        arranged on the support,    -   a material measure with optical elements that is movable        relative to the sensor head and can be mounted on a moving part        of a device, for example a motor, and can interact with the        sensor head for determining an absolute position value,

wherein the sensor head is arranged movably on the support, and meansare provided for moving the sensor head relative to the support by adefined amount.

The movable arrangement of the sensor head on the support has theadvantage that the absolute position of a moving element, e.g. of ashaft or of some other machine component, can be determined in itsposition at rest. Therefore when the machine is started, the absoluteposition of the machine component can be determined in a very shorttime, without requiring movement of the machine component itself, e.g.to reach a reference mark first. Furthermore, in combination with acompact sensor head described below, products can be developed that aremuch smaller and more economical than devices of this kind known fromthe prior art.

The position measuring device may be is characterised in that thedisplacing means for moving the sensor head is formed by a motor, whichis linked mechanically to the sensor head.

Furthermore, it may be that the material measure is a rotary encoder.

An advantageous method is also to be disclosed for determining theabsolute position of a moving element in the position at rest by meansof a position measuring device, which enables the absolute position ofthe component to be determined by means of a material measure that ismovable relative to a sensor head, and is coupled to the movableelement,

characterised in that,

for determining the absolute position of the movable element in theposition at rest, the sensor head is displaced relative to the movableelement.

According to an embodiment, it is a position measuring device with

-   -   at least one material measure with an optical structure, such as        an arrangement of 3-D reflectors,    -   a light source arranged at a distance from the material measure        and    -   at least one light receiver arranged at a distance from the        material measure, and    -   at least one transparent substrate present between the material        measure and the light receiver,    -   wherein on the side of the substrate turned away from the        material measure, the light receiver is deposited directly on        the transparent substrate in the form of a thin-film structure        consisting of several layers arranged one above another,    -   wherein a light source is provided at a distance from the light        receiver, and    -   wherein a supporting plate is provided, on which the substrate        is arranged.

The light receiver thus has, advantageously, the form of a thin-filmsensor. In the aforementioned layers, a recess is provided for a lightsource. The light source may be designed so that it can be made alongwith the processes for production of the sensors (light receiverelements), so that the dimensions and position of the light receiversand of the light source are predetermined by a lithography mask.Moreover, the light source can be formed by a diaphragm and an LED or byan OLED deposited directly on the substrate. In contrast to the priorart described at the beginning, therefore no further adjustmentoperations are necessary, which greatly simplifies the production of theposition measuring device, but also makes it more reliable.

The light source may be arranged behind a recess or diaphragm etched outof the aforementioned layers.

Furthermore, a decoding circuit can be provided, which is arranged onthe supporting plate.

The supporting plate may have circuit-board conductors on both faces, onthe one hand for contacting with the light receiver and on the otherhand for contacting a decoding circuit. Furthermore, it is advantageousif the supporting plate has terminals for connecting the positionmeasuring device to an external display.

The transparent substrate and the supporting plate are advantageouslyfirmly joined together by Flip-Chip assembly.

According to another advantageous embodiment, the light receiver is incontact with a metallic covering layer, such as aluminium. Theelectrically conducting metal may be aluminium, which may be alloyedwith 1 to 5% titanium. Furthermore, it is desirable if the electricalconnection between the conducting covering layer and the circuit-boardconductors of the supporting plate is made by means of solder globules,so-called “bumps” or “stud-bumps”. The connection between the metalliccovering layer or the bumps on the one hand and the supporting plate onthe other hand may be produced by means of an electrically conductingadhesive.

According to another variant of the invention, a permanent resist isprovided between the supporting plate and the substrate for delimitingthe spread of the adhesive.

According to an embodiment, the thin-film sensor is formed by

-   -   a transparent conducting layer, such as a transparent conducting        oxide layer (=TCO layer),    -   a first doped layer,    -   an intrinsic layer, such as an amorphous silicon layer,    -   a second doped layer and    -   an electrically conducting, metallic covering layer,

wherein the layers may be present in the order stated. Advantageously,for producing a structured sensor zone, the aluminium layer, theuppermost doped layer and at least one part of the intrinsic layer maybe etched away regionally.

The device according to the invention can also be characterised in thatthe light receiver is formed as a sensor zone consisting in each case ofa plurality of light receiver elements, which are connected togetherelectrically. Advantageously, in the device at least one first and onesecond sensor zone are provided, said zones being assigned to a materialmeasure with an incremental track and an index track or an absolutetrack.

The first sensor zone may have first and second light receiver elements,which are interlocking. Furthermore it may be advantageous if the firstand second light receiver elements are roughly U-shaped. The geometriccentre of gravity of the first and second light receiver elements of thefirst sensor zone should be roughly on a straight line. It can also beenvisaged that the first sensor zone is in each case formed by aplurality of strip-shaped light receiver elements, said light receiverelements being arranged at an angle of between 0.5 and 15 degrees to oneanother and one after another in a specified direction. The even and theodd (with respect to their sequence) light receiver elements can in eachcase be connected together electrically-conducting. According to anotherconfiguration of the device, the first and/or the second light receiverelements are connected together by an additionally appliedelectrically-conducting layer, wherein an insulating layer is providedbetween the metal layer and the additional, conducting layer. The firstand second light receiver elements of the first sensor zone may bearranged so that two alternating signals, displaced by 180 degrees, areobtained in the order “AbaB”.

The aforesaid device can be further characterised in that the secondsensor zone is provided for the production of an index, and astrip-shaped, first light receiver element and two second light receiverelements, positioned at an angle from the first light receiver element,are formed. The geometric centre of gravity of the surface of the firstlight receiver element and of the surface of the two second lightreceiver elements of the second sensor zone advantageously essentiallycoincide. According to another configuration of the device according tothe invention, the material measure has two tracks with opticalelements, wherein a first track serves for producing an incrementalsignal and the second track serves for determining a position number oran index signal.

Some features relating to the light source, which can be implementedindividually or in combination, are as follows: the light source can bearranged behind the substrate. In addition it is advantageous if thelight source is an LED. Furthermore, the light source can be arrangedessentially in the same plane as the light receiver. The light source,such as an OLED, is formed directly on the substrate between the lightreceivers. According to another configuration the light source isembedded in a metallic layer, so that scattered light can be kept out.There can also be an air gap in the light path between light source andsubstrate.

According to another advantageous embodiment of the present invention,the decoding circuit is arranged on the other side (i.e. on the sideopposite to the light receivers and/or the light source) of thesupporting plate in the form of an integrated circuit for processing thelight receiver signals (such as in the Flip-Chip process), wherein thelight receivers are connected electrically to the integrated circuit.

The aforementioned supporting plate consists of ceramic or of plastic(e.g. polyimide). According to another variant the supporting plate canbe made of plastic film, such as polyimide film.

A method of producing a sensor head for a position measuring device canbe particularly advantageous when it has the following process steps:

a) applying a large number of groups of light receivers on a transparentsubstrate in a thin-film process, said groups of light receivers servingin each case for the production of a single sensor head,

b) providing in each case a diaphragm for a group of light receivers,

c) applying contact points on the light receiver, such as in the form ofspheres, so-called “bumps” or “stud bumps”, which are made of solder orbetter still of gold, and can be applied by an electrolysis process(e.g. directly on bare Al-pads),

d) providing a supporting plate with circuit-board conductors or contactpoints, which correspond to the contact points of the light receivers,and

e) joining the glass substrate and the supporting plate together usingan electrically conducting adhesive.

The contact points can also be applied in the form of gold spheres,so-called “stud-bumps”, or in the form of gold deposits or gold/nickeldeposits.

A non-electrically-conducting layer, which has recesses that correspondto the contact points of the light receivers, can be applied on thesupporting plate beforehand. The recesses can then be filled at leastpartially with the electrically conducting adhesive.

A decoding circuit can be applied on the back of the supporting plate.

Furthermore, it is advantageous if some of the spaces present betweenglass substrate and supporting plate are filled with an underfill.

The material measure may be a rotary encoder or a rotary encoder isprovided, which has a stated material measure.

Furthermore, a position measuring device has—especially in combinationwith one or more of the aforementioned features—the followingcomponents:

-   -   a housing,    -   a sensor head arranged in the housing with a light source and a        light receiver element,    -   a rotatable encoder, which can be mounted on a shaft of a        device, such as a motor,    -   a reflective material measure with optical elements, provided at        a distance from the sensor head, said material measure being        arranged on the rotary encoder, wherein the material measure is        arranged advantageously on the side of the rotary encoder that        is opposite the housing.

The sensor head may be mounted on a printed-circuit board, which has akeyed connection to the housing, via a snap connection.

Furthermore, it is desirable for the position measuring device to havean adapter part, which has

-   -   a first fastener for connecting to the device and    -   a second fastener for keyed connection to the housing,    -   wherein the second fastener is a snap connection,    -   wherein the snap connection is formed by one or more projections        on the adapter part and one or more recesses in the housing.

The housing advantageously has an assembly bearing, in which the rotaryencoder and/or a seating for a shaft connected to the rotary encoder ismounted. The assembly bearing can be for example a ball bearing andespecially a Teflon bearing.

The contacting of the sensor head takes place, according to anembodiment, via a lateral opening in the housing, wherein the opening isarranged on the side of the sensor head opposite to the rotary encoder.The contacting can take place via one or more cables, which pass throughthe opening, wherein they may be ribbon cables and especially aFlexprint.

Furthermore, it may be advantageous if the housing has a recess on theside, which connects to the opening, wherein the recess extends from theopening along the side up to another side or a rim or an edge of thehousing and/or wherein the recess extends from the opening to the topside of the housing.

In another configuration variant the material measure has at least twotracks, wherein one track is an incremental track and wherein a secondtrack is either an index track or a code track.

A position measuring device (such as an encoder) can—especially incombination with one or more of the stated features—have the followingcomponents:

a) a housing,

b) a sensor head with one or more light receiver elements arranged inthe housing, and

c) a rotatable material measure with optical elements, provided at adistance from the sensor head. The material measure may be arranged on arotary encoder, which can be mounted on a shaft of a motor or some otherdevice.

The light receiver element is arranged in a defined or predeterminedposition relative to the optical elements and interacts with these toproduce a signal. According to the invention, said defined position ofthe light receiver element relative to the optical elements isestablished by a sensor head holder, which has a keyed connection withthe sensor head. The sensor head holder also has a keyed connection withthe housing. Furthermore, the housing may be arranged in a definedposition relative to the material measure and/or to the opticalelements.

In this case the sensor head holder can be the support described above,on which the sensor head is arranged and which for the purpose of movingthe sensor head is connected operatively with a motor.

The term “position” refers in this document to the distance and/or theorientation of the aforementioned part of the device, in particularrelative to other parts of the device. The deviation from the definedpositions is advantageously less than 0.2 mm, less than 0.1 mm or lessthan 0.05 or 0.02 mm. This means that the corresponding parts of thedevice have been manufactured with the aforesaid accuracy.

According to an advantageous configuration, the position measuringdevice is characterised in that the light receiver element is arrangedon a substrate, the edge of which has a keyed connection with the sensorhead holder. Furthermore, the light receiver element may be applied onthe substrate by a thin-film process. The substrate is advantageously atransparent substrate and may be a glass substrate.

When the light receiver element or the light receiver elements areapplied on a substrate, the exact position of the light receiverelements relative to the edge of the substrate and therefore to a partof the sensor head can already be established in the production process.Light receiver elements can be applied particularly easily by thin-filmprocesses. In this case a substrate board is provided with a largenumber of light receiver elements and is then divided into smaller units(substrates). This dividing can be carried out very accurately, e.g. bysawing the substrate board. This results in a defined position of thelight receiver elements relative to the edge of the substrates, i.e. theplace where the dividing took place.

It is advantageous if the sensor head holder has a first structuralelement, which has a keyed connection with the sensor head, wherein thefirst structural element is an opening. Furthermore, it is advantageousif the sensor head holder has a second structural element, which has akeyed connection with the housing, wherein the second structural elementmay be the edge of the sensor head holder. The first structural elementis in this case advantageously arranged in a defined position relativeto the second structural element. The first structural element can nowhave a keyed connection with the edge of the substrate.

This means that the position of the light receiver elements relative tothe optical elements on the material measure may be established viaseveral parts of the device that are matched to one another in theirdimensions (substrate, sensor head holder, housing, material measure).The advantage is that there is no need for mechanical adjustment duringassembly. The sensor head holder thus acts like an adapter. The sensorhead holder can be made as part of the housing and/or of the coverdescribed below. The sensor head holder is made as a separate part ofthe device, as this facilitates manufacture and assembly.

According to an advantageous embodiment of the invention, the sensorhead holder is arranged between the material measure and a cover thatseals the housing. The cover may be in contact with the sensor headholder and fixes it with respect to its position in the housing. An edgeis provided inside the housing, to form a support for the sensor headholder, and if the sensor head holder is fixed between this support andthe cover.

In a method of production of a position measuring device, a sensor head,which has one or more light receiver elements, has a keyed connectionwith a sensor head holder. The sensor head holder has a keyed connectionwith a housing. The sensor head holder is in this case introduced orinserted into the housing. The housing is arranged in a predetermined ordefined position relative to a material measure, wherein the materialmeasure is rotatable and has optical elements. In this case the housing,the sensor head holder and the sensor head have been or will be designedso that their keyed connection establishes a defined position of thelight receiver element relative to the optical elements.

Furthermore, it may be advantageous if in said method

-   -   the light receiver element is applied on a substrate,    -   the edge of the substrate has a keyed connection with the sensor        head holder, if the sensor head is connected to the sensor head        holder,    -   the light receiver element is applied on the substrate by a        thin-film process, and    -   the substrate is a transparent substrate and especially a glass        substrate.

It may also be desirable if, in the aforementioned method

-   -   the sensor head holder is formed with a first structural        element, which has a keyed connection with the sensor head, when        the sensor head is connected to the sensor head holder, wherein        the first structural element may be an opening (a through-hole),        and    -   the sensor head holder is formed with a second structural        element, which has a keyed connection with the housing, when the        sensor head holder is connected to the housing, wherein the        second structural element may be the edge of the sensor head        holder, and    -   the first structural element is formed in a defined position        relative to the second structural element.

Finally it is also desirable if, in the method

-   -   the sensor head holder is inserted in the housing at a distance        from the material measure and has a keyed connection to the        housing,    -   on the side of the sensor head holder opposite to the material        measure, the housing is sealed with a cover, and    -   the cover may be brought in contact with the sensor head holder,    -   wherein the cover and/or the housing and/or the sensor head        holder are separate parts of the device.

Owing to the compact design of the sensor head, it is possible tomanufacture shaft encoders with further properties, for example positionsensors with several sensor heads for the redundant acquisition ofposition values. Another possibility is to construct very compactabsolute encoders, with a Manchester code or similar serial codes or apseudorandom code incorporated in the material measure.

The aforesaid codes can for example be formed as binary codes. Throughthe concatenation of two optical elements that are differently orientedrelative to their optical axis, and that interact with suitable receiverelements, two different states or signals can be produced. The aforesaidsignals or states can be correlated with the increment signal. Thedetermination of an absolute position value will be made possible by arelative movement between sensor head and material measure, in which thesequence of the optical elements is determined.

These advantageous properties are best achieved when the materialmeasure is formed from semicircular-cylindrical reflectors and the lightsource has defined dimensions. This once again presupposes exactpositioning of the light source above the light sensor, in order toobtain stable and reliable signals. The bundling of the total amount oflight incident on a division of the material measure, together with thecompact sensor head, make it possible to construct position determiningunits that have a high luminous efficiency and therefore a low powerconsumption, and ensure the function of the encoder with lower lightoutput. The position measuring device according to the invention istherefore most suitable for use in battery-powered appliances.

The use of a thin-film structure with an intrinsic layer has theadvantage that reliable light receivers can be produced with simplemeans owing to the presence of an interlayer that is insulating initself. These layers have low dark currents and are particularlysuitable for constructing a sensor head for an encoder that can operatewith little current.

The aforesaid methods can also comprise, as process steps, the use ofone or more of the aforesaid features of the device according to theinvention (or the functions made possible by these features).

Advantages of configurations of the position measuring device describedhereunder are:

-   -   the possibility of manufacturing a position measuring device        economically with the desired necessary precision,    -   constructing a position measuring device with minimum        dimensions, with high accuracy and reliability. This is        advantageous especially in the medical area for optical        examination instruments, in which for example a mirror must be        positioned exactly.    -   providing a position measuring device that tolerates a certain        installation tolerance and nevertheless can ensure reliable        operation and    -   providing a position measuring device whose design is        insensitive to environmental influences.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail on the basis of the drawingsand a exemplary embodiment. The drawings show:

FIG. 1 schematically and in a perspective view, the design principle ofan encoder, consisting of a sensor head according to the invention and amaterial measure located at a distance from the sensor head;

FIG. 2 schematically, the structure of the sensor head consisting ofglass substrate with sensor zones formed thereon, a supporting plate andan evaluator, which are in each case joined together in the Flip-Chipassembly process;

FIG. 3 the individual process steps for producing the sensor zones andcontacting thereof;

FIG. 4 the individual process steps for constructing the light source;

FIG. 5 schematically, assembly of the components on a wafer substrate;

FIG. 6 in cross-section, a exemplary embodiment of an encoder arrangedin a housing for small motors;

FIG. 7 schematically, how with relative movement of receiver element andmaterial measure, the light intensities recorded by the receiver elementare converted into an analogue signal and then to a digital signal forposition determination;

FIG. 8 schematically, the production of an index signal by means of asingle optical element and two receiver elements;

FIG. 9 schematically, the production of a position signal by means oftwo different optical elements, which are concatenated according to aManchester code, and two receiver elements;

FIG. 10 a top view of a first exemplary embodiment of a sensor headaccording to the invention with a plurality of receiver elements with anincremental and an index track;

FIG. 11 a top view of a second exemplary embodiment of a sensor headaccording to the invention, in which the receiver elements areelectrically connected by means of a separate circuit-board conductor;

FIG. 12 an embodiment of the invention with a light source with an LED,which is arranged behind a diaphragm, wherein the diaphragm essentiallydetermines the dimensions of the light source;

FIG. 13 a circuit for optimum assignment of the index signal Zb formedby the material measure;

FIG. 14 a exemplary embodiment of an absolute encoder with cold-startposition determination;

FIG. 15 a perspective view of a kit encoder with motor;

FIG. 16 a rear and side view of the housing with horizontal cable;

FIG. 17 a sectional view of the housing of the kit encoder

FIG. 18 a design of the shaft support.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 shows an encoder 10 according to the invention comprising asensor head 11 and a material measure 13, which is movable relative tothe sensor head 11 in a direction 15. The first and second sensor zone29, 35, which are at a distance 40 from the material measure 13, arearranged on the back of the sensor head 11. “Material measure” means, inthe context of the present invention, a graduation or scale, which ismounted on a support or carrier and is suitable for reflecting andmodulating a light beam, when the material measure is moved relative tothe sensor head. This material measure can take the form of a circularrotary encoder or an oblong beam. The material measure itself has adivision, wherein each division is suitable by definition for modulatinga light beam, when the division is moved through the light beam.Structures are known, for example, in which for example one half of thedivision is transparent and the other half is opaque. Advantageously,each division is represented by a reflective optical element, which issuitable for bundling a light beam (e.g. hollow cylinder, hollowmirror). However, the use of grating structures is also conceivable, buttheir efficiency in light processing would be lower than that ofmirrors, by which the light beam is deflected.

The sensor head 11 shown consists essentially of a supporting plate 17and a transparent substrate 19, on the back of which, i.e. the sideopposite the supporting plate 17, a light source 21 and light receiverelements 23 are arranged. The light source 21 emits a light beam, whoseprincipal axis is designated with the reference number 22. A lightsource is used, which emits light in the visible region. For a betterlight signal with a smaller deflection, light with a wavelength below630 nm, especially 580 and 630 nm, or below 460 nm would beadvantageous. The material measure 13 contains at least one first track25 with first optical elements 27, which interacts with a first sensorzone 29 of the material measure 13. Next to the first track 25,according to the exemplary embodiment shown, a second track 31 isprovided, with at least one individual optical element 33. This secondtrack 31 interacts with a second sensor zone 35 of the sensor head 11.As can be seen from FIG. 1, the optical elements 27 of the materialmeasure are arranged in one plane, which is essentially parallel to thefaces 37 of the substrate. Moreover, the material measure 13 is arrangedrelative to the substrate 19 in such a way that the tracks 25, 31coincide, in each case in a direction parallel to the axis 22 of thelight beam, with the sensor zones 29, 35.

The optical elements 27, 33 are formed as focusing lenses or mirrors,which in each case reflect incident light bundled onto the sensor head11. According to the exemplary embodiment shown, the optical elements27, 33 have the form of a circular semi-cylinder. The first track 25serves for production of an incremental position signal, and the secondtrack 31 for production of an index signal, as is described in moredetail below (description for FIGS. 7 and 8).

The position of the material measure relative to the sensor head(especially the distance 40, cf. FIG. 1) is usually associated with anassembly tolerance, which has a direct influence on the quality andreliability of the measuring signal. With assembly tolerance of zero,the faces 37 of the substrate 19 are parallel to a plane passing throughthe material measure 13, and the direction of motion 15 (corresponds toa tangent to a circular path in the case of a material measure providedon a circular disk) runs at right angles to a longitudinal central axis39, which divides the sensor zones 29, 35 and the light source 21 intotwo segments in each case. Deviations from the exact relativeorientation of material measure 13 and substrate 19, which are indicatedin FIG. 1 with arrow 41, can displace the position signals 104 from thetwo tracks 25 and 31 towards each other (see below, description for FIG.10). At zero tolerance, the centre line 43 of the material measure willrun essentially parallel to an axis 45 passing through the centre of thelight source 21, provided the sensor zones 29, are arrangedsymmetrically to the centre of the light source. At zero tolerance ofthe distance between material measure 13 and sensor head 11, the nominaldistance is mainly determined by the design of the optical elements 27,33 of the material measure 13. In the context of the present invention,focusing optical elements and especially three-dimensional (3D)reflectors are especially advantageous, because these are particularlytolerant with respect to variation of the distance between materialmeasure 13 and substrate 19.

With this arrangement, 3-channel encoders can be made with the width ofa division from 18 μm to 150 μm. In the case of an encoder with ahousing diameter of about 20 mm this corresponds for example to a numberof marks on the rotary encoder from 360 to 3000 and in the case of anencoder with a housing diameter of about 6 mm this would correspond to anumber of marks from 64 to 380 (a mark can be defined for example by anoptical element or a division).

According to FIG. 2, the sensor head 11 according to the inventioncomprises the substrate 19 with the first and second sensor zones 29,35, the supporting plate 17 and an evaluator 47 mounted on thesupporting plate 17. Substrate 19, supporting plate 17 and evaluator 47are joined mechanically rigidly together by means of adhesive andunderfill and sealed against the environment. The light source 21 is anLED, which is arranged behind a diaphragm, which defines the size of thelight source. It is important for the present invention that the sensorzones 29, 35 are deposited directly on the substrate in a multistagethin layer process, by which the sensors and the diaphragm 49 are formedin one etching process. This method of production has the advantage thatthe relation between diaphragm 49 and sensor zones 29, 35 can beestablished very precisely, so that they can be formed in one etchingstage according to FIG. 3 b and FIG. 4 b.

Electrical connection between the first and second sensor zones 29, 35and the supporting plate 17 is provided by means of Flip-Chip assembly.So that the heat-sensitive sensor zones 29, 35 cannot be damaged duringthe production process—which could happen if “bumps” of solder were tobe used—for the electrical contacts so-called “stud bumps” orultrasonically applied gold spheres 53 are applied on the uppermostsensor zone 51 formed from aluminium (FIG. 3 e). Once again,circuit-board conductors 55 are provided on the supporting plate 17.Above these circuit-board conductors 55, a film 57 is applied, which atthe site of the planned electrical connection has recesses 59, which arefilled with conductive adhesive 54 (FIG. 3 e) before assembly. Substrate19 and supporting plate 17 can now be joined together by means ofFlip-Chip assembly. In the non-conducting layer 57, there are recesses59 at the intended contact points. Various plastics, e.g. epoxymaterial, are suitable as film formers. After bonding, the space betweensupporting plate 17 and glass substrate 19 is filled with a so-called“underfill”.

The decoding circuit 47, e.g. an ASIC, is arranged on the back 63 of thesupporting plate 17. Connection of the decoding circuit 47 to thesupporting plate 17 can also be effected by Flip-Chip assembly as withconnection between the glass substrate 19 and the supporting plate 17.For this purpose, circuit-board conductors 64 and a non-conducting layer65 with recesses 67 are applied on the back 63. The recesses 67correspond to the contact points of the decoding circuit 47. These arefilled with an electrically conducting adhesive before the supportingplate 17 and the decoding circuit 47 are joined together. Thethrough-contacting from front to back takes place by means of openings69 in the supporting plate 17, which are filled with a conductingmaterial, e.g. solder or an electrically conducting adhesive.

As can be seen from FIG. 2, the light source 21, e.g. an LED, is housedin a recess 71 of the supporting plate 17. A spacer 75 keeps the lightsource 21 at a distance from the glass substrate 19, so that an air gap77 is provided between the light opening and diaphragm 49. The air gap77 serves for reducing the internal reflection present in the substrate19, so as to achieve better utilization of the luminous energy. The backof the LED light source 21 can be contacted by means of an electricallyconducting adhesive 79 (FIG. 4 e).

In particular, the manner of production of the sensor zone and of thediaphragm 49 in thin-film technology is important for application of thepresent invention. In this, in a first step all layers that are requiredfor constructing the sensor zones are deposited on a large area on atransparent substrate, a glass substrate (FIG. 3 a). The size of theglass substrate is selected in such a way that a large number, inparticular more than 200, more than 2,000 or more than 10,000 sensorarrangements can be fabricated simultaneously. Selection of substratesize depends on the available coating and etching devices.

In the manufacture of the light receivers, the following layers areapplied successively on the glass substrate 19 (FIG. 3 a), whichproduces the structure of a PIN diode:

1) a conducting transparent layer 81, a TCO (=transparent conductingoxide) layer, with a layer thickness between 10 and 100 nm, between 20and 70 nm or between 25 and 50 nm.

2) a first n− or p+ doped layer 83 with a layer thickness between 10 and80 nm, between 20 and 70 nm or between 25 and 50 nm.

3) an intrinsic layer 85 with a layer thickness between 100 and 1,500nm, between 200 and 1,000 nm or between 400 and 800 nm.

4) a second p+ or n− doped layer 87 with a layer thickness between 10and 80 nm, between 20 and 70 nm or between 25 and 50 nm and

5) a conducting top layer 51 with a layer thickness between 100 and2,000 nm, between 500 and 1,500 nm or between 700 and 1,200 nm. In theregion of the contact points 89, 91, or in the region of the pads 111(cf. FIG. 10) the layer thickness is 1,000 nm.

The various layers are deposited by CVD (chemical vapour deposition),PECVD (plasma-enhanced chemical vapour deposition) or similar, modifiedprocesses such as VHFCVD or HWCWD. A plasma-enhanced chemical vapourdeposition is comprised of silane, in order to produce an aSi:h(amorphous silicon) intrinsic layer. For doping the layers, the silanehas an admixture of other gases, which contain the metals germanium(e.g. GeH) and/or boron (e.g. BH).

After the glass substrate has been coated with the aforementionedlayers, the shape and extent of the light receiver elements and of thelight source are defined, by applying a photoresist on the uppermostlayer 51, exposing this to UV with a mask, and dissolving away eitherthe unexposed or the exposed regions. Then in a first etching step, forexample by ion beam etching on the places where the photoresist wasdissolved away, the conducting covering layer 51, the second doped layer87 and a part of the amorphous silicon layer 85 can be removed. As aresult, the structure of the light receivers is already formed (FIG. 3b). Instead of amorphous silicon, similar materials could also be used,which can be used for forming a PIN diode.

Then in a further step, in certain places the TCO layer is laid bare, bycompletely etching away the amorphous silicon layer 85 and the firstdoped layer 83 essentially in a second etching step (ion beam etchingand/or “reactive ion beam etching” (RIE)), or modified methods) (FIG. 3c). The procedure can be similar to the first etching process, i.e. theplaces that are not to be processed are masked first and then thenon-masked places are processed. These process steps are very familiarto a person skilled in the art, so that there is no need to go into moredetail here. The places that were laid bare form, after removal of theamorphous silicon layer, the one electrical contact point 89 of thelight receiver. The other contact point 91 is formed by the conductingcovering layer 51.

Then the sensor zone is coated with a protective layer 93, an SiO₂ layer(FIG. 3 d). The contact points 89, 91 are in each case recessed byetching or by the lift-off process. It should also be pointed out thatFIGS. 3 and 4 serve exclusively for illustrating the production processand that the layer thicknesses shown do not coincide with the actuallayer thicknesses.

As can be seen from FIG. 4, the diaphragm used in this exemplaryembodiment for forming the light source can be produced by the sameprocess steps as were used for producing the light receiver structuresand the contacts. The light opening 49 is applied in the second etchingstep (FIG. 4 c), in that a place that was already etched partially inthe first etching process is etched further or completely. Through thislight opening 49, the light can pass unhindered into the substrate 19.Any further (non-transparent) layers, such as the Al layer 51, also havean opening at the same place, so as not to prevent the light passingthrough. In this way a diaphragm is formed, which advantageouslyrestricts the propagation of light from the LED 21, or defines the sizeor the dimensions of the light source.

The LED can be glued onto the uppermost layer 51, by placing it on aspacer 75 (also see FIG. 12). The spacer 75 provides a defined gapbetween the substrate 19 and the light source 21. In this way a cavityis defined (reliably) for the adhesive 79. The spacer will be 4 to 50 μmhigh, 6 to 12 μm high, or formed from permanent resist.

Finally, the sensor zones and the supporting plate 17 are connectedtogether electrically by Flip-Chip assembly. In the same process step,the front of the light source is contacted with the metal layer 51, inwhich circuit-board conductors, which are not shown in more detail, havebeen formed (contact point).

The thickness of the glass substrate 19 can be about 1 mm. The thicknessis between 0.4 and 0.6 mm, wherein a glass substrate with a thickness ofabout 0.16 mm can be used for high-resolution encoders.

FIG. 5 shows an arrangement of a large number of adjacently arrangedsensor heads on a large supporting plate 97 in the form of a wafer. Thediagram shows the substrates 19, which are fastened by Flip-Chipassembly on the carrier material 97. The carrier material is a board ofelectrically non-conducting material, on which, in a prior coatingprocess, both on the front and on the back, circuit-board conductorswere applied for contacting a large number of substrates 19 with lightreceivers and decoding circuits 47. The light sources 21 can be appliedbeforehand either directly, e.g. by gluing, on the glass substrate 19,or can be integrated in a recess of the carrier material 97. Then thedecoding circuits 47 can be placed on the back of the carrier material97. Assembly of the decoding circuit 47 can also take place in theFlip-Chip process. The substrate 19 with the light receiver elements 23and the decoding circuit 47 can be connected simultaneously to thesupporting plate 17. When the sensor heads 11 or the glass substrates 19have been contacted with the decoding circuits 47, the encoder functioncan already be tested. This can take place in an automated process. Onlyafter that, the carrier material 97, which is scribed (grooves 98), isbroken up, sawn or separated by means of a grinding disk, intosupporting plates 17. The carrier material is ceramic, especiallyblack-coloured ceramic.

On a lateral edge of the carrier material 97, two recesses 99 areprovided, in which pins 96 of a tool can engage. By means of therecesses 99 and corresponding tools, the carrier material 97 can beaccurately aligned during the various process steps. This allowseconomical manufacture.

FIG. 6 shows an example of a miniature motor, on which, owing to thecompact design of the sensor head, a high-quality sensor can be mounted.If, on the material measure, there is an absolute track according toFIG. 9 and an incremental track according to FIG. 7, an absolute encodercan be constructed in the same construction volume and the sameconstruction. In this case a movement of less than about 2° issufficient for the absolute position to be determined or to be read fromthe material measure by means of the sensor head. With encoders of thecurrent state of the art (with an index mark), an angular motion of upto 360° is necessary for an absolute reference point to be found.

FIG. 6 shows an encoder 10 with a sensor head 11 and a rotary encoder155, on the surface of which a material measure (not shown) is arranged.The rotary encoder 155 is connected to a shaft 157 and is thereforerotatable. The sensor head 11 and the material measure formed fromoptical elements (not shown) interact to produce a signal. For this, inthis configuration the sensor head 11 has a light source 21, which emitslight towards the material measure. The optical elements of the materialmeasure are arranged on the side of the rotary encoder 155 opposite thesensor head 11. They reflect the light coming from the light source 21in bundled form onto the sensor head 11, where it is recorded by thelight receiver elements (not shown). Naturally, the light source canalso be arranged on the other side of the rotary encoder 155 and cansend the light via the optical elements to the sensor head 11. However,the solution is shown, in which the sensor head 11 has both one or morelight sources and one or more light receiver elements. For correctformation of the position signals, the light receiver elements must bearranged in a defined position relative to the optical elements. Insteadof adjusting the position of the light receiver elements relative to thematerial measure or to the housing directly with a tool and/or anoptical device, as known from the prior art, in the encoder shown 10this is achieved indirectly by matching the dimensions of the individualparts of the device with one another. The sensor head holder 141 has afirst structural element in the form of an opening 149, into which apart of the sensor head 11 can be inserted with an accurate fit, so thata keyed connection is produced. This part of the sensor head 11 isadvantageously a transparent substrate 19, onto which the light receiverelements are applied by thin-film processes. In these processes, a largenumber of light receiver elements are placed on one substrate board,which is then cut up into (smaller) substrates 19. Such a design of thesensor head 11 allows the position of the light receiver elementsrelative to the edges of the substrates to be determined by the accuratecutting of the substrate board. The edge 151 of the substrate 19 caninteract as a keyed connection with the aforesaid opening 149 in thesensor head holder 141. The opening 149 is positioned accuratelyrelative to a second structural element, which is in this case the edge153 of the sensor head holder 141. The edge 153 of the sensor headholder 141 interacts as a keyed connection with the inside wall of thehousing 143, wherein the housing 143 is once again arranged in a definedposition relative to the material measure. This means that the positionof the sensor head 11 or of the substrate 19 and therefore also theposition of the light receiver elements relative to the optical elementson the material measure is established indirectly via several parts ofthe device, which are matched with one another in their dimensions. Theadvantage is that no mechanical adjustment is required during assembly.The sensor head holder 141 thus also acts as an adapter. Regarding theaforesaid dimensions or the defined positions, advantageously deviationsof less than 0.2 mm, less than 0.05 mm are ensured, which is generallysufficient for correct functioning of the measuring device. The housing143 is sealed with a cover 145, which presses against the sensor headholder 141 and thus fixes it in the housing 143. The housing 143 has,between cover 145 and housing 143, an opening, through which contactingof the sensor head 11 e.g. by means of cables 159, or by means of aFlexprint, can take place. This arrangement ensures simple assembly ofthe sensor head. According to the configuration variant of an encoder 10shown in FIG. 6, an adapter for the rotary encoder 155 is provided onthe shaft 157. The adapter has a seating for the shaft and a flange 241extending from the shaft 157 radially outwards. The adapter has ahollow-cylindrical shaft support and an annular flange 241, protrudingfrom the shaft support. The rotary encoder 155 is in contact with theside of the shaft support opposite the shaft 157 and with the flange 241of the adapter, the rotary encoder has one or more feet 240, which inthe assembled state of the encoder 10 come in contact with the flange241. The rotary encoder 155 is fastened on the adapter with adhesive.This arrangement ensures simple assembly of the sensor head.

The rotary encoder 155 is glued onto the shaft 157. The through-hole 272in the rotary encoder is configured (cf. FIG. 18) so that one or morechannels 275 (for example 2-20 or 3-10) are formed between the rotaryencoder and the shaft 157, and become filled with adhesive. FIG. 18shows one design of the through-hole 272 of a rotary encoder 155,wherein the rotary encoder has a keyed connection with the shaft 157 viaflat regions 271. Correspondingly, those parts of the edges of thethrough-hole 272 that form the channels 275 are farther (in particular0.02 to 0.2 mm farther) from the shaft, than those parts of the edgesthat form the flat regions 271. The latter are in contact with theshaft, i.e. the flat regions represent the contact points between rotaryencoder 155 and shaft 157. The channels 275 between rotary encoder andshaft 157 can be filled with adhesive. This arrangement is especiallyadvantageous from the standpoint of the toolmaker, as it enables him toproduce a tool for providing a through-hole 272 very easily. Said toolis advantageously made from a (circular-cylindrical) workpiece, whichhas a diameter that is 0.02 to 0.2 mm larger than the diameter of theshaft 157. The workpiece can be provided in several places e.g. bygrinding, with flats or with flat sides, which form the flat regions 271during production of the through-hole 272. According to a configurationvariant, 1 to 10, especially 2 to 5 or 3 channels 275 are provided.

The rotary encoder and the material measure are formed from plastic,black-coloured plastic, for easier visual inspection. The materialmeasure is then coated with a metal, such as gold or aluminium. However,an additional protective layer, e.g. SiO₂ or synthetic resin, can beapplied on the aluminium layer.

An alternative embodiment envisages a film structure of the rotaryencoder. A plastic can serve as the carrier material, on which analuminium layer and a plastic film as oxidation protection of thealuminium layer are provided. The material measure can be formed by hotembossing on the side of the aluminium layer.

FIGS. 7, 8 and 9 show various embodiments of material measures 25/31 andlight receiver elements 23, which serve for forming at least oneanalogue signal 103. The analogue signals 103 a and 103 b are processedin a decoding circuit and optionally converted into a digital signal 104that can be processed further. The output signals from the decodingcircuit serve for determining the position of the material measurerelative to the sensor head. The position data can be evaluated by meansof an analogue or digital signal.

FIG. 7 shows an incremental track, FIG. 8 shows the track for forming anindex, which is evaluated at least once per revolution, and FIG. 9 showsanother track structure, which is encoded according to the Manchestercode, which together with the incremental signal can define an absoluteposition. The three tracks mentioned can form, alone or in combination,the material measure, which can be integrated on a carrier, for examplea rotary encoder, and is made in the same operation as the carrier. Thematerial measure is formed with two tracks, wherein the optical elementsof both tracks have the same focal length.

The track 25 of the material measure shown in FIG. 7 consists ofidentical optical elements, which are arranged at regular distances fromone another in the direction of motion 15 (incremental track). These areoriented the same or parallel relative to the principal direction of thelight reflected from them. In FIG. 7, the optical elements aresemicircular-cylindrical reflectors, which represent the embodiment inthe context of the present invention. The light emitted from the lightsource is bundled by an optical element of the material measure and isfocused on the plane of the sensor 100. There, the light is incident ata point 108. However, little or no light is incident on the adjacentregion 107 of the plane of the sensor. The distribution of the lightintensity on the plane of the sensor is represented by curve 101. Point101 h of the curve corresponds to a high energy density, and point 101 tcorresponds to a low energy density. The electrical conversion of thelight intensity into an electrical signal takes place with at least twolight receiver elements 23, which are arranged with 180° mutualdisplacement. This means that always when one light receiver elementregisters a maximum, the other light receiver element registers aminimum, and vice versa. With the two light receiver elements, twoanalogue signals 103A+ and 103A− are produced, which are sent to thedecoding circuit for further processing. The decoding circuit can thenform a digital signal 104 from the analogue signals 103.

FIG. 8 shows the index track 31 of a material measure consisting of asingle reflector, roughly semicircular-cylindrical in cross-section,which is centred about the axes 105. The width of this reflector will bebetween 100% and 300% of the width of a reflector of the incrementaltrack. On the plane of the sensor 100, the light is bundled essentiallyat a point 108, wherein only very little light is incident on theadjoining region 107. An essentially constant and unmodulated amount oflight is incident on the remaining region 109. The distribution of thelight intensity on the plane of the sensor 100 is represented by curve101, wherein point 101 h corresponds to a high energy density and point101 t corresponds to a low energy density. The conversion of the lightintensity into an electrical signal takes place with a specialarrangement of light receiver elements 23. According to an embodimentthe light receiver elements 23 consist of a main receiver 23Z+ and tworeceivers 23Z−, which are arranged symmetrically to the main receiver23Z+ and are connected together electrically. Advantageously, the totalarea of the light receiver 23Z− is at least 10%, at least 20% or atleast 30% greater than the total area of the main receiver 23Z+. This isimportant in connection with the evaluation of the signals. Because thearea contents of the two light receiver elements Z+/Z− are different, itcan be ensured that signal 103 a is well away from signal 103 b, so thatthey can never cross in the remaining region 109. With this lightreceiver arrangement, two analogue signals 103 a and 103 b are produced,which are processed further in the decoding circuit. The signals can forexample be compared in a comparator circuit, wherein a point ofintersection of the two signals produces in each case a change of thedigital level, i.e. one of the flanks of the pulse Zb (cf. digitalsignal 104).

For forming a stable digital pulse 104 it is important that the twosignals 103 a and 103 b intersect with a large slope. This is achievedwith the special arrangement of the light receiver elements 23: In thecentral position according to FIG. 8 the bundled light beam is mainlyincident on the middle receiver element 23Z+, so that the signal peak103 aa is formed. So that the signal level 103 ba is as low as possible,the two light receivers Z− should, for example at point 107, receiveless light than normally, i.e. than when the light beam is notmodulated. This is achieved because the obliquely positioned lightreceiver elements formed on the upper part, i.e. at the proximal end,are somewhat wider than at the distal end. The configuration of thereceivers 23Z+,23Z− shown, with a first oblong light receiver element23Z+ and two second oblong light receiver elements 23Z−, which arearranged essentially with mirror-image symmetry and at an angle to thelongitudinal axis of the first receiver element 23Z+, can be regarded asoptimum. With this form of the light receiver elements, signals 103 aand 103 b can be formed that have a large slope at the points of mutualintersection, so that a reliable basic signal Zb can be formed for theindex signal.

The light receiver elements Z− (“Z minus”) are arranged obliquelyrelative to the light receiver element Z+ (“Z plus”). At their endsopposite the light receiver element Z+, the light receiver elements Z−have a width that is much smaller than the width at their ends facingthe light receiver element Z+. This optimum arrangement means thatduring the motion of the index lens (optical element on the materialmeasure) in the direction 15, regions of medium, low and high lightintensity are moved over the sensor zone. The form of the light receiverelements Z− means that the variation in light intensity does not affectthe signal to the same extent at every position of the index lensrelative to the sensor zone. In the edge region, i.e. where the narrowend of the light receiver element Z− detects, the light intensity has aless pronounced effect on the signal than in the central region, i.e. atthe site of the light receiver element Z+ and where the wider end of thelight receiver element Z− is. Another factor is the distance from thelight source. The narrow ends of the light receiver elements Z− arefarther from the light source and so receive a lower light intensity.

The geometric centre of gravity 102 b of the two light receiver elements23Z+ and 23Z− coincides as far as possible at the same point. If thecentres of gravity do not coincide, i.e. if they are some distanceapart, then the level ratio between the two signals 103 a and 103 bchanges when the distance between the material measure 13 and thesubstrate 19 changes (see FIG. 1). Owing to the advantageous geometry ofthe receiver elements 23 described, the distance between materialmeasure and sensor head can vary over a relatively wide range, withoutadversely affecting the signal quality, so that the rather largetolerance in the axial position of shafts of small motors can be takenup without any problem. This also has the advantage that expensiveadjustments are not required.

FIG. 9 shows a track 31 of the material measure (absolute track). Thetrack contains, like the incremental track shown in FIG. 7, a largenumber of optical elements, but here, the optical elements are not allaligned identically or regularly or (relative to their optical axis) notall parallel. Each of the optical elements is configured and/or arrangedso that it focuses the light either onto a first or a second point onthe plane of the sensor. The two points represent the 0 (zero) or the 1(one) of a binary code. The sequence of zeroes and ones (binary digits)defines a code, e.g. an 8-bit code, in which 8 successive binary digitsdefine a characteristic position number, which occurs only once on thematerial measure or over the length of the material measure. In thepresent example, one point is to the left of the axis 105 and the otheris to the right of it. It is, however, also possible to provide three ormore different points, i.e. arrange and/or configure the opticalelements correspondingly, so that the sequence of the differentlypositioned points of incidence 108 on the plane of the sensor 100 forexample forms a ternary code. However, a binary code such as a so-calledManchester code may be used. On the plane of the sensor 100, the lightis bundled at a point 108, which is in each case arranged asymmetricallyto the axis 105. Only a small amount of light then falls on region 107.The distribution of the light intensity on the plane of the sensor isshown by curve 101. The electrical conversion of the light intensityinto an electrical signal takes place with at least two light receiverelements 23, arranged mutually displaced by 180 degrees. With the lightreceiver elements 23, two analogue signals 103 a and 103 b are produced,which are fed together with an incremental signal to a decoding circuit.The decoding circuit will, with the aid of the incremental signal,evaluate the signals 103, so that the bit value of the division isdetermined and is outputted in a digital signal.

Advantageously, two channels (A and B) and, per channel, two lightreceiver elements 23 as described above, are provided. It should benoted that in FIGS. 7 and 9, for clarity, only the light receiverelements 23 for one channel (A or B) are shown in each case.

For a given direction of motion or rotation of the material measureaccording to 15, the bit value is read on each rising or each fallingflank of the two incremental signals, on every fourth flank of bothincremental signals (from channels A and/or B), by reading thedifference between signal 103 a and 103 b at this time point. At thistime point, the level of the digital signal 181 is adjusted according tothe bit value or the bit value is outputted in some other way. It canalso be envisaged that the reading of the bit value in a direction ofrotation or direction of motion of the material measure takes place forexample with falling flank of channel A and with rotation or movement inthe opposite direction with rising flank of channel A.

The two incremental signals form 4 flanks per division (two analoguesignals 103 a/103 b per channel A/B). Which of these flanks is used forevaluating the bit value depends ultimately on the placement of thesensor head within the permissible tolerance field relative to arotation about the angle 41 (cf. FIG. 1). The angular error can becorrected with the circuit shown in FIG. 13.

As mentioned above, the order of the bit values of the material measureis selected in such a way that with a particular number of successivebits, a particular order can only be found once over the length of thematerial measure. The order is formed according to Manchester code.

FIG. 10 shows an arrangement of the light receiver elements 23 for a3-channel encoder (channel A, channel B, channel Z or index), whereinthe principal axis 45 of the emitted light beam passing through thecentre of the light source coincides with the centre line 43 of thematerial measure (FIGS. 1, 2) (see FIG. 1). The light receiver elementsfor the incremental signal are arranged in the sensor zone 29 (whichinteracts with the first track 25 of the material measure) and those forthe index signal are arranged in sensor zone 35 (which interacts withthe second track 31 of the material measure). At the contact point oropenings 91 (see also FIGS. 3 d and 3 e) the “stud-bumps” can bearranged on the uppermost metal layer (cf. 51 in FIG. 3 a), e.g. byultrasonic welding. These points can be covered with a layer of gold, sothat when using a conducting adhesive, the adhesiveness is not impairedby an oxide layer. The same sensor head could also be used for anabsolute encoder with Manchester code, wherein region 25 then remainsunchanged and at least two receiver elements (as shown for example inFIG. 9) are arranged in region 31.

So that the encoder is not sensitive to assembly tolerances (i.e. withrespect to the centring of the light source and the angular position ofthe sensor head relative to the principal axis 43 (cf. FIG. 1) of thematerial measure), the following order of the light receiver elementsrelative to the direction of motion 15 is selected: A+/B−/A−/B+ orA−/B+/A+/B−, i.e. with reference to the two channels A and B, asymmetrical arrangement of the light receiver elements relative to theaxis 39. In this case the light receiver elements A+,A− and B−,B+ are ineach case offset by 180 degrees. In this way, both for channel A and forchannel B, two sinusoidal curves, mutually displaced by 180 degrees, areobtained, which can be converted in a comparator circuit into a digitalsignal. In this arrangement, the contact points and the linkage betweenthe light receiver elements 23 are formed in the same or from the samematerial as the light receiver elements, i.e. these regions are alsooptoelectronically active. It is then necessary to bear in mind that thecentre of gravity of each of the 4 light receiver elements in the sensorzone 29 is essentially at the same distance from the light source 21(see line 102). Here, the points 102 b mark in each case the centre ofgravity of a U-shaped receiver element. In direction 15, the distancesbetween the centres of gravity 102 b should essentially coincide withthe division of the material measure. The normal width 114 of a lightreceiver in sensor zone 29 is selected between 40 and 80% of the widthof a division of the material measure. Width is to be understood, inthis context, as that dimension of the light receiver elements or of thelight source that runs parallel to the principal axis 45. In order toobtain the centre of gravity of an array of light receiver elements inthe correct place, it is generally necessary to make the width of thereceiver elements wider at certain places 106, or adjust the width. Thisis because the transition lines 115 within the light receiver elementsand the areas around the contact points or openings 91 also detectlight, i.e. inevitably increase the areas of the light receiverelements. This has a negative influence on the position of the centresof gravity 102 b of the light receiver elements and the signal produced.The reference number 110 shows the contacts to the TCO layer.

Advantageously, the width of the light source 21 or of the diaphragm 49is selected between 60 and 150%, or 100% to 120% of the width of adivision. If the width of the diaphragm 49 is too small, too littleluminous energy is allowed through. If the width of the diaphragm 49 istoo large, the width of the light spot will be too large, so that thesignals become too flat to be evaluated reliably.

An identical arrangement of the light source and of the optical receiverelements could be achieved with other technologies, if for example thelight source 21 were to be constructed as a light-emitting OLED on thesubstrate 19, and the sensor zones 35 and 29 were to have a similarlayer structure as the OLED. Both OLED and the light receiver elementsthen consist of thin layers, as shown in FIG. 3 a, but differentstarting materials could be used.

FIG. 11 shows another arrangement of light receiver elements, whereinthe individual receiver elements are connected electrically by VIAs 112(“vertical interconnect access”) through the passivation layer (e.g. anSiO₂ layer or an SiO₂/Si₃N₄ layer structure) with conducting tracks,such as of aluminium, applied on the passivation layer. The advantage ofthis arrangement is that the light receiver elements 23 are optimallyconfigured, without the transition lines 115 and/or contact points 91being able to influence the formation of the analogue signals, orwithout the need for corrections of the width 114. At the end of theconducting tracks there are the pads 111, on which the “stud-bumps” areapplied. Such a solution will cost more, because additional layers mustbe provided and additional precautions must be taken. An arrangement ofthe receiver elements 23 in the direction of motion 15 has the sameadvantages as given above in the description of FIG. 10. Connection tothe TCO layer can also be made by means of the conducting tracks and aVIA 112, wherein once again pads 111 can be arranged at the end of theconducting tracks for reliable application of a stud-bump.

FIG. 12 shows a design of the light source consisting of diaphragm andLED (also see FIG. 2). The LED is, as described in FIG. 4 c, glued onthe substrate 19 (e.g., glass), or on the uppermost metal layer (cf.FIG. 3, 51), and radiates through the light opening 49 that was made inthe thin-film structure. The LED 21 is housed in recess 71 (cf. FIG. 2)of the supporting plate 17 (cf. FIG. 2). Several variants of how thelight source can be mounted on the substrate 19 are shown. FIG. 12 ashows the light source with an emission layer 161 and a contact layer163. Between the light source 21 and the coated glass substrate 19, aspacer 75 is provided, which keeps the light source at a distance fromthe substrate 19. It can be seen that with this design there is the riskthat light emerging laterally 165 will impinge on the light receiver,i.e. this arrangement is disadvantageous because the scattered lightproduced can penetrate into the light sensor zone, which can lead todeviations from the desired signal quality. The reference number 170shows the cone of light emitted from the light source towards thematerial measure.

FIG. 12 b shows an isolated light source, in which the emission layer161 is edge-coated with a non-transparent covering layer 167. This canprevent scattered light impinging on the light receiver. According toFIG. 12 c, the non-transparent covering layer 167 is not applied on thelight source 21 but on the light receiver. This covering layer serves inthe example also as contact 163 to the LED. Further precautions mayconsist of selecting, as “underfill”, a material that is opaque or haslow transmission for light.

FIG. 13 shows a circuit with which assembly errors with respect to theangular position 41 (cf. FIG. 1) of the sensor head relative to theprincipal axis of the material measure can be compensated, so that theindex signal can function reliably regardless of said angular error. Asdescribed above, selection of the flank of the incremental signal fordetermining the bit value (in connection with an absolute track) dependson the placement of the sensor head or on the rotation thereof by theangle 41. The circuit can therefore be used for determining theseflanks.

FIG. 13 a shows the signals A, B, Zb and Z. Signal Z is formed bycombining signals A and B and Zb. A and B each correspond to a digitalsignal 181 (cf. FIG. 9; only signal for one channel shown), whereinsignal A originates from channel A and signal B from channel B. Thesignal Z depicted in said FIG. 13 a consists of two pulses, whichbasically is undesirable. By recombining the original signals A and B,in FIG. 13 b other signal states Aout (or Ao) and Bout (or Bo) areproduced, wherein the signal Zb is almost centred on the region of thesignals A and B in plus. The resulting signal Z therefore consists of asingle pulse.

The conversion (recombination) of the original signals A (or Ain) and B(Bin) into the effective output signals Aout and Bout is effected usingthe control signals X1 and X2, e.g. according to the combination tablein FIG. 13 c, wherein the original signals A and B are inverted and/orinterchanged.

The two channels A and B in FIG. 13 b consist for channel A of theinverted input channel B and for channel B of the input channel A.Therefore combining the signals from channel Aout and channel Bout andchannel Zb forms an index signal Z with a single pulse. Further signalcombinations are shown in the truth table 13c.

Signal processing according to the truth table can take place by thecircuit illustrated (FIG. 13 d). The circuit is controlled by twocontrol signals X1 and X2. The signals Ain 200 and Bin 201 are invertedby two inverters 206, 207. The circuit additionally contains 4mutliplexers 208, which depending on the state of the control signalsX1, X2 relay one of the two signals in the input to the respectiveoutput. In the examples presented in FIGS. 13 a and 13 b, the controlsignals are set at X1=0 and X2=1, where the travels are shown withthicker lines in FIG. 13 d. The control signals X1 and X2 are producedin the decoding circuit. The decoding circuit is designed so thatvarious settings or values for the control signals can be programmed in,which can take place during final product inspection.

In FIG. 14, a special design of an absolute encoder is shownschematically, which can determine an absolute position signal even withstationary sensor head 11 or stationary shaft 157, or in cold start.This is made possible by a special device, which allows relativemovement between material measure and sensor head. The device has aswivel arm 182 (or an equivalent device), on which the at least onesensor head is secured. The swivel arm is driven by a motor, andproduces a relative movement between material measure 13 and sensor head11, which corresponds to a fraction, less than 5 degrees, of a completerevolution. The absolute position can be determined by evaluating thesignals coming from the sensor head 11. Once again, this is possibleowing to the compact design of the sensor head and thetolerance-friendly design of this arrangement.

FIG. 14 shows the schematic construction of the absolute encoder with ahousing 143, 145, a mounted shaft 157, a rotary encoder 155 with amaterial measure 13 with an absolute track according to FIG. 9 and anincremental track according to FIG. 7, a carrier 182 that is fixed orcan be swivelled through a small angle, on which at least one sensorhead 11 is applied. The rotary encoder 155 is secured centrally on ashaft 157, said shaft in a housing 143 having a keyed connection with atleast one bearing 180.

With a small movement of the axis or a movement of the rotary encoder ofless than 3 degrees, a position number can be determined, with which an(absolute) position value of the rotary encoder can be determined. Thenthe position value can be determined either by addition/subtraction ofthe pulses from the incremental track or by determining further positionnumbers. Redundant acquisition of the position values can easily beachieved by combining the two variants.

The Manchester code is read with one or more pairs of receiver elements(see FIG. 9). A position number is determined between 1 and a maximumnumber of position numbers by a movement of the material measurerelative to the sensor head. The length of the position number,expressed in binary form, is the number of bits, which is determined bythe length of the material measure. The position number is determined byreading a number of successive bits. A position number is defined by thematerial measure formed according to the Manchester code. On the entirelength of the material measure, the position numbers are singular, i.e.determine in each case the position of the material measure relative tothe light receivers. The position number read is converted into aposition value by means of the decoding circuit. The position number istransferred by means of digital signals 181 and converted by aconversion circuit 187 into a position value. The conversion circuit 187can be integrated in the decoding circuit 47 (also see FIG. 2).

Redundant determination of the position values can protect againstreading errors, by recording several successive position numbers. Thismeans that in fact a “lengthened” position number is recorded. Thelengthened position number is converted into several position values. Ifthe position values cannot be arranged in a row, it could be concludedthat there is a reading error of the Manchester code.

FIG. 14 shows an arrangement in which the conversion circuit 187 isarranged outside of the sensor. The conversion circuit 187 is connectedby 3 lines 186 to the encoder, or its decoding circuit (schematicrepresentation). Two lines transmit the pulses from channels A and B(digital signal 104) and the third line transmits a digital signal 181,which forms the position numbers of the absolute track. In this way,position information is transmitted redundantly between encoder 10 andconversion circuit 187. This ensures reliable transmission of theposition numbers and determination of the position values. Theconversion circuit 187 transmits, by means of a conventional data bus189, e.g. SPI, I2C, Profibus etc., the data for example further to anSPS control system. The conversion circuit 187 comprises amicroprocessor 188, which performs translation of the position numbersinto position values. Translation of the position number into a positionvalue can take place in two different ways:

a) a Manchester code generator forms position numbers successively; whenone of the position numbers from the material measure to be translatedcoincides with the generated position number, the position number of thegenerator is outputted as position value,

b) in the microprocessor, a table is provided, which contains positionvalues, wherein each storage location in the table or each positionvalue is associated with a particular position number, so that positionnumbers can be assigned to particular position values.

A disadvantage of conventional encoder systems with Manchester code isthat for determining the absolute position, a relative movement of thematerial measure, and therefore a movement of the machine components tobe measured, is necessary, in order to determine the absolute positionvalues. This is not appreciated by the machine builder.

It is desirable to be able to determine a position value on switching onthe machines, before any movements take place. This is solved in thatthe rotary encoder has a large number of tracks, with at least onereceiver element assigned to each track. The circuit required for thisis complex and such a multi-track arrangement takes up a lot of space,so that position measuring devices of this kind do not fit into smallhousings.

In another embodiment of the invention, means are provided that allowmovement of the sensor head relative to the material measure internallyin the sensor, so that determination of the position value becomespossible by pressing a button, without having to set the machine inmotion. This is achieved by turning the sensor head or the carrier (e.g.a swivel arm 182) on which the sensor head is arranged, through approx.3°. This can for example take place with a motor 185 and a cam 184,which engages as a keyed connection in a slot 183 of the swivel arm 182.Instead of a motor with lever and cam, actuators of a different kind canbe used. The signals produced by this movement (channel A, channel B andM-code) can then be used for determining the position values.

FIGS. 15 to 17 show a position measuring device. This is a kit encoder10, which is of an especially compact design. This design ischaracterised by a particular arrangement of the rotary encoder 155, ofthe material measure 13 applied thereon, of the housing 143 and of thesensor head 11, which interacts with the material measure 13 to producea signal. The material measure 13 is in this case located on the side249 of the rotary encoder 155 that is opposite the housing 143. Thismeans a part of the housing 143 extending next to, along or essentiallyparallel to the flat side of the rotary encoder 155 and/or the upperpart of the housing 143. Thus, the rotary encoder 155 is arrangedbetween the inside of the housing 143 (or the inside of the aforesaidpart of the housing) and the sensor head 11 or the printed-circuit board251. Based on the fact that the support 267 for the shaft (or at leastthe larger part, especially at least 70 or 90% of the length of theshaft support) is arranged on the same side of the rotary encoder 155 asthe material measure 13, there is a considerable saving of space. Thereason for this is that the place of measurement, i.e. the regionbetween material measure 13 and sensor head 11, is arranged next to theshaft or the shaft support 267. During assembly of the rotary encoder155 in the housing 143, the position of the rotary encoder 155 relativeto the aforementioned part of the housing 143 parallel to it, or thedistance between the inside of the housing 143 and the rotary encoder155, are established by pressing in or deforming the aforesaid parallelpart of the housing 143, and releasing it again after installing therotary encoder 155. To make this easier, the material of the housing 143on the aforesaid part that runs parallel to the rotary encoder 155 canbe thinner or more elastic than the adjacent parts. Advantageously, thesensor head 11 is mounted on a printed-circuit board 251, which has akeyed connection with the housing 143. The printed-circuit board 251 canalso be designed to assume the function of the supporting plate.

This takes place by means of a snap connection 153. Very simple assemblyof the encoder 10 can be achieved by using an adapter part 255, whichhas a first fastener 257 and a second fastener 259. The first fastener257 serves for securing the adapter part 255 relative to the shaftcentrally on the motor 243 and can for example consist of screws. Thesecond fastener 259 is advantageously a snap connection 259, which isformed for example by one or more projections 261 and one or morerecesses 263. Projections 261 and recesses 263 can be arranged on thehousing (especially on the inside wall of the housing) and/or on theadapter part 255. It is a detachable connection. Advantageously, thehousing 143 has an assembly bearing 265, for receiving the rotaryencoder 155 and/or a support 267 for a shaft that is connected to therotary encoder 155. This is because the rotary encoder 155 and the shaftsupport 267 can be formed either as one piece or can also be individualparts that are connected together. The assembly bearing 265 has thefunction of keeping the rotary encoder central to the housing during theassembly operation. The bearing itself can be a ball bearing or asliding bearing made of Teflon, wherein the sliding bearing may be usedas the rotation of the motor shaft is not loaded by such a bearing.

The function of the assembly bearing is to ensure accurate alignment ofthe rotary encoder and of the sensor head (cf. axis 22 in FIG. 1). Thebearing material Teflon has the advantage of a low coefficient offriction and especially pronounced creep behaviour, so that the bearingfunction in the assembled state is lost over time. This is desirable asthe assembly bearing should lose its bearing function after assembly, sothat the existing bearing system is not subject to any additionaldisadvantageous loading. It is also possible to use a rigid bearing(e.g. ball bearing), which is, however, advantageously connectedelastically to the printed-circuit board 251.

The radius of the rotary encoder 155 is smaller than the radius of theprinted-circuit board 251. If the outer edge of the sensor head 11relative to the rotation axis of the rotary encoder 155 is furtheroutside than the outer edge of the rotary encoder 155, the rotaryencoder 155 can be of smaller design and space is left e.g. for thecables mentioned below or the recess 273. In the encoder 10 according tothe invention, the housing 143 and/or the printed-circuit board 251and/or the rotary encoder 155 and/or the fasteners 253 and/or 259 aremade of plastic. An especially compact design is achieved, moreover,when the contacting of the sensor head 11 takes place via a lateralopening 269 in the housing 143. This opening 269 is arrangedadvantageously on the side of the sensor head 11 and/or of theprinted-circuit board 251 opposite the rotary encoder 155. Thus, thecontacting can take place on the underside of the sensor head 11 or—whenthe sensor head 11 is contacted via the printed-circuit board 251—on theunderside of the printed-circuit board 251. The aforesaid contacting canbe effected by means of one or more cables 159, which enter the housing143 through the opening 269. Advantageously, it is a ribbon cable 159 asshown in the diagrams, wherein a Flexprint can also be used. The opening269 is therefore advantageously of oblong shape and is arrangedessentially parallel to the rotary encoder 155 and/or to theprinted-circuit board 251. The ribbon cable 159 is also correspondinglyoriented. If the housing 143 has, on a side 245, a recess 273 adjoiningthe opening, this is especially advantageous. Especially when the recessruns from the opening along the side 245 of the housing 143 up toanother side 247 or up to a rim of the housing 143 or up to an edge ofthe housing 143. The recess 273 can run from the opening 269 e.g. up tothe top 245 of the housing 143. The cable 159 can thus be positioned inthe recess 273. If the housing 143 is of a cylindrical shape, the cable159 is thus within the cylinder radius. Furthermore, it is advantageousif the position measuring device, or the encoder 10 has one or more ofthe features such as are described in other parts of this document. Wemay mention in particular the configuration of the sensor head 11 and ofthe material measure. The material measure has for example at least twotracks, wherein one track is an incremental track and wherein a secondtrack is either an index track or an encoded track, as described in thisdocument.

The parts shown in FIG. 17 together form a component of a device, whichcan be inspected or tested before shipment from the factory. Togetherwith the fastener 255 (cf. FIG. 15) the aforesaid component of a deviceforms an assembly kit, which can for example be fitted on a motorwithout particular expense.

FIG. 18 shows an advantageous connection technology for securing arotary encoder 155 on a shaft 157. The rotary encoder has a through-hole272 with a special shape, for example a cylindrical shape with 3 (ormore) flat or flattened regions 271. The rotary encoder is arrangedcentrally on the shaft 157, by inserting the shaft 157 into thethrough-hole 272. The mounting of a plastic rotary encoder on a metalshaft is not so simple, when the requirements relating to concentricitytolerances and interference fit are considered. An excessiveinterference fit can lead to breakage of the rotary encoder made ofplastic. Moreover, this may not happen until after a certain timeperiod, i.e. for example several months after assembly. Theconcentricity tolerance directly impairs the quality of the encoderfunction. This arrangement is advantageous especially for the toolmaker.He can adjust the centring of the parts most accurately by grindingflats on the tool punch. The spaces or channels 275 provide room foradhesive, which in combination with a very easy interference fit canavoid the risk of cracking and ensures a reliable connection of the twoparts.

1-12. (canceled)
 13. A position measuring device, comprising: at leastone material measure having an optical structure comprising a pluralityof focusing optical elements; at least one light receiver arranged at adistance from the material measure; a light source arranged at adistance from the material measure and at a distance from the lightreceiver; and at least one transparent substrate present between thematerial measure and the light receiver, wherein the light receiver isdeposited directly on the transparent substrate, on the side of thesubstrate opposite the material measure in the form of a thin-filmstructure consisting of a plurality of layers arranged one aboveanother; and a supporting plate comprises a plurality of circuit-boardconductors, the transparent substrate and the supporting plate arejoined solidly together by a Flip-Chip assembly, the material measurehas two or more tracks with optical elements, wherein a first trackserves for production of an incremental signal, and the light receiveris formed as a sensor zone, each comprising a plurality of lightreceiver elements, wherein at least one first and one second sensorzones are provided, wherein the first sensor zone is configured tointeract with the first track for producing an incremental signal andwherein the second sensor zone is configured to interact with a secondtrack, which is a coded track.
 14. The position measuring device ofclaim 13, wherein the light source and the light receiver comprise asensor head and wherein the material measure is movable relative to thesensor head.
 15. The position measuring device of claim 14, wherein thematerial measure is mounted on a movable element, the sensor head isarranged on a carrier, and the sensor head is displaceable relative tothe movable element when the movable element is in a resting position.16. The position measuring device of claim 14, further comprising amotor mechanically linked to the sensor head for displacing the sensorhead.
 17. The position measuring device of claim 14, wherein the carrieris configured to swivel for displacing the sensor head.
 18. The positionmeasuring device of claim 14, wherein the carrier is rotatable about aswivel point.
 19. The position measuring device of claim 18, wherein thecarrier is rotatable about the swivel point by an angle of less than 5degrees.
 20. The position measuring device of claim 13, wherein thesecond sensor zone has at least one first and one second light receiverelement, wherein the first light receiver element is configured forproduction of a first signal and the second light receiver element isconfigured for production of a second signal.
 21. A method fordetermining the absolute position of a moving element in a position atrest, comprising: using a position measuring device comprising a sensorhead and a material measure movable relative to the sensor head, whereinthe material measure is coupled to the movable element; and determiningthe absolute position of the movable element in a resting position withthe position measuring device by displacing the sensor head relative tothe movable element.
 22. The method of claim 21, wherein the materialmeasure has two or more tracks with optical elements, wherein a firsttrack is an incremental track, and a second track is a coded absolutetrack.
 23. The method of claim 22, wherein the sensor head has at leasttwo light receiver elements, which interact with the coded absolutetrack of the material measure, and wherein a first light receiverelement produces a first signal and a second light receiver elementproduces a second signal.
 24. The method of claim 21, wherein during thedisplacing, the sensor head moves along a circular arc.
 25. The methodof claim 24, wherein the absolute position of the movable element in theresting position predetermined at a centre-point angle of the circledefined by the circular arc of less than 5 degrees.